With the advancement of wireless communication, different wireless communication systems have been developed, such as mobile communication system, wireless local area network (WLAN) and wireless personal area network (WPAN). For example, the mobile communication system may be Global System for Mobile Communications (GSM), 3rd Generation (3G) or Long Term Evolution (LTE) or Worldwide Interoperability for Microwave Access (WiMAX), the WLAN may be Wi-Fi, and the WPAN may be Bluetooth. Preferably, the different wireless communication systems operate on different operation frequency bands and use different communication technologies (e.g. modulation, coding and/or ciphering), to avoid mutual interference between wireless signals of the different wireless communication systems. However, some of the wireless communication systems must operate on the same operation frequency band due to limited spectrum resources.
For example, operation frequency bands of Bluetooth (e.g. IEEE 802.15.1) and Wi-Fi (e.g. IEEE 802.11) are on the industrial, scientific medical (ISM) band located around a carrier frequency of 2.4 GHz, and the ISM band is reserved internationally for industrial, scientific and medical applications. Therefore, there may be wireless communication devices using Bluetooth and Wi-Fi on the same operation frequency band at the same time. In this situation, when a wireless signal of Bluetooth or Wi-Fi is transmitted and received via an antenna, a wireless signal of the other must stop to be transmitted and received via the same antenna even though different protocols with different modulations and codings are respectively used for Bluetooth and Wi-Fi. In other words, transmission or reception of the wireless signal of Bluetooth or Wi-Fi occupies the antenna.
In addition, wireless signals of the same communication standards may correspond to different operation frequency bands. For example, the operation frequency bands of Wi-Fi are 2.4 GHz and 5 GHz, and wireless signals corresponding to 2.4 GHz and 5 GHz can contain different data and can perform transmission with different communication device. However, wireless signals corresponding to 2.4 GHz and 5 GHz have to be transmitted or received by one of a plurality of antennas in a conventional wireless communication device. In other words, the wireless signals corresponding to 2.4 GHz and 5 GHz cannot select different antennas according to channel qualities, such as signal-to-noise ratio (SNR) and bit-error-rate (BER), corresponding to the antennas transmitting and receiving the wireless signal. In such a condition, the transmission of the conventional wireless communication device may be inefficient.
Therefore, how to select an antenna for each wireless signal according to the channel qualities and operation frequency bands of each wireless signal has become a topic to be discussed and addressed.